WASHINGTON — Vice President Joe Biden will appear this week for the first time before the largest gathering of progressive activists in the country, a critical constituency for any Democrat with presidential ambitions.

Biden’s debut at the annual Netroots Nation comes as the vice president has made a number of moves that could better position himself with the liberal wing of the Democratic Party, if he decides to make a third run for the presidency.

Those moves could help him compete for liberal support with Sen. Elizabeth Warren of Massachusetts if she runs for the Democratic nomination, and stake out the left flank of Hillary Clinton.

Among Biden’s steps:

• At a June White House summit on working families — as presumed Democratic front-runner Clinton grappled with missteps on talking about her wealth — Biden portrayed himself as a populist everyman, declaring he was once “the poorest man in Congress.”

• In Philadelphia to mark the Fourth of July, he declared gay marriage to be the “civil rights issue of our day.”

• And in South Carolina he delivered a closed-door speech that was fiery and populist, attendees told CNN.

“Clearly there’s a part of him that wants to run for president,” Robert Borosage, president of the liberal group Campaign for America’s Future, said in an interview. “I think he’s kind of testing the water, putting a toe in, and Netroots would be a good place for that.”

The Scranton, Pa., native’s blue-collar roots make him an attractive candidate for the party’s liberal base, which is increasingly focused on income inequality and what it sees as the excesses of Wall Street, Borosage said. Biden also declared his support for gay marriage before President Barack Obama.

“On domestic policy, he’s always been standup,” Borosage said. “It doesn’t seem like a contradiction for him to appeal to progressives.”

Biden does have challenges with the left. He is viewed as hawkish on foreign policy, and like Clinton he voted in 2002 to give President George W. Bush the authority to go to war in Iraq, a vote he has since said he regrets.

Biden is widely viewed as wanting to keep his name in play, telling interviewers earlier this year that he was unlikely to make a decision on a presidential bid until next summer, but that it was “as likely I run as I don’t run.”

Confidantes say the current 2016 speculation is premature and that Biden is simply speaking to rally troops who are part of the administration’s natural constituency.

“This is what vice presidents do,” said Ted Kaufman, a longtime Biden aide who was appointed to finish out Biden’s Senate term when Biden left for the vice presidency. “It’s safe to say there isn’t anything he’s doing right now that isn’t part of his job description.”

Kaufman notes Biden’s remarks about his income aren’t new: He used similar language to describe himself in 2008, and the Obama campaign touted his less-than-millionaire status to cast him as someone who could relate to the middle class.

“I’m not sure what his aspirations are for running, but one thing I hope is the center of his remarks is getting people tuned back into 2014,” Brooks said. “If people don’t turn out for 2014 and they don’t work as hard as a presidential year, then the administration is going to be handed a Congress that’s even worse. I know it’s fun to speculate on 2016, but we still have to work to do this year.”

Still, Brooks notes Biden’s appearance “certainly serves a dual purpose for him if he decides to run. Getting out there and being the guy most able to most openly court the liberal base certainly doesn’t do him any harm and in fact does him some favors for 2016.”

Biden won’t be the only potential 2016 candidate to mingle with the estimated 3,000 activists and bloggers at the Cobo Center in Detroit.

Warren, who says she’s staying in the Senate but remains a favorite among liberals for a presidential bid, will make her third Netroots appearance. She will deliver the conference’s keynote address on Friday, a day after Biden speaks.

Clinton, who is widely believed to be considering a run but has largely eschewed political events in lieu of her book tour, will not attend. But her campaign-in-waiting, Ready for Hillary, will be at the event, sponsoring a party and parking its bus at the convention center.

Clinton remains formidable despite a rocky roll-out of her latest book, with a recent poll finding that she’d sweep the Democratic primary field for the 2016 presidential race with 58 percent of the vote.

Warren came in at 11 percent and Biden was at 9 percent in the Quinnipiac University Poll.

“If Mrs. Clinton does not run, there will be a real hard-fought battle by people who, with the exception of Biden, are virtually unknown to most American voters,” said Quinnipiac pollster Peter Brown. “If he wants to run in 2016, Democratic primaries are decided disproportionally by liberal voters, and this is a pretty good group of liberal voters.”